Microscopic origin of the magnetic easy-axis switching in Fe3GaTe2 under pressure

The two-dimensional layered ferromagnet ${\mathrm{Fe}}_{3}{\mathrm{GaTe}}_{2}$, composed of a $\mathrm{Te}\text{\ensuremath{-}}{\mathrm{Fe}}_{\mathrm{I}}\text{\ensuremath{-}}{\mathrm{Fe}}_{\mathrm{II}}\text{/}\mathrm{Ga}\text{\ensuremath{-}}{\mathrm{Fe}}_{\mathrm{I}}\text{\ensuremath{-}}\mathrm{Te}$ stacking sequence, hosts two inequivalent Fe sites and exhibits a high Curie temperature and strong out-of-plane magnetic anisotropy, making it a promising platform for spintronic applications. Recent experiments have observed a pressure-induced switching of the magnetic easy axis from out-of-plane to in-plane near 10 GPa, though its microscopic origin remains unclear. Here, we employ first-principles calculations to investigate the pressure dependence of the magnetocrystalline anisotropy energy in ${\mathrm{Fe}}_{3}{\mathrm{GaTe}}_{2}$. Our results reveal a clear easy-axis switching at a critical pressure of approximately 10 GPa, accompanied by a sharp decrease in the magnetic moments arising from ${\mathrm{Fe}}_{\mathrm{I}}$ and ${\mathrm{Fe}}_{\mathrm{II}}$ atoms. As pressure increases, spin-up and spin-down bands broaden and shift oppositely due to band-dispersion effects, leading to a reduction in net magnetization. Simultaneously, the spin-orbit coupling (SOC) contribution from ${\mathrm{Fe}}_{\mathrm{I}}$, which initially favors an out-of-plane easy axis, diminishes and ultimately changes sign, thereby promoting in-plane anisotropy. The SOC contribution from the outer-layer Te atoms also decreases steadily with pressure, although it retains its original sign; this additional reduction further reinforces the in-plane magnetic easy axis. In contrast, ${\mathrm{Fe}}_{\mathrm{II}}$ atoms continue to favor an out-of-plane orientation, but their contribution is insufficient to counterbalance the dominant in-plane preference at high pressure. These findings elucidate the origin of magnetic easy-axis switching in ${\mathrm{Fe}}_{3}{\mathrm{GaTe}}_{2}$ and provide insights for tuning magnetic anisotropy in layered materials for spintronic applications.